1. Field of the Invention
The present invention relates to a stepping motor driving apparatus capable of detecting out-of-phase (loss of synchronism) and an image forming apparatus having such a driving apparatus.
2. Related Background Art
In mechatronics systems having electric driving sources, a motor driving apparatus for driving a stepping motor being rotated while switching its exciting phases successively under open loop control is sometimes used. Recently, due to cost effectiveness, such a technique has widely been used.
In the open loop motor control, since it is not required to effect feedback of information such as rotational angle and rotational speed of the motor obtained from a sensor such as an encoder or a tachometer generator, such a sensor can be omitted.
However, when the sensor such as the encoder is omitted, for any reason, it is difficult to detect a phenomenon (a phenomenon of loss of synchronism; referred to merely as xe2x80x9closs of synchronismxe2x80x9d hereinafter) that the rotation of the stepping motor does not synchronous with a phase exciting signal.
Accordingly, in the system having the stepping motor subjected to the open loop control, detection of the loss of synchronism of the stepping motor is performed by providing a sensor and by detecting the fact that a driven object is not moved nevertheless the motor is being rotated by the sensor.
However, in the system using the stepping motor, since the sensor for detecting the fact that the driven object is not moved to recognize occurrence of the loss of synchronism is required, cost is increased. Further, since the detection of the loss of synchronism effected by the sensor is an indirect detecting method in which motion of the driven object driven by the stepping motor is detected to judge presence/absence of the loss of synchronism, it takes a relatively long term until the loss of synchronism is judged.
Accordingly, the detection of the loss of synchronism of the stepping motor in a sensor-less and high speed fashion give the great merit to the system. On the other hand, a micro-computer has widely been used in a motor control field due to low cost, electric power savings and multi-function.
In conventional image forming apparatuses such as copying machines, a sheet conveying apparatus in which a DC motor is used as a drive source in a sheet conveying system through which a recording paper (sheet) is actually passed and a plurality of conveying rollers in the sheet conveying path are driven via a transmitting mechanism such as gears and/or an electromagnetic clutch was widely used. In such a sheet conveying apparatus, sheet conveying control was effected by controlling the sheet conveying rollers by energizing or disenergizing the electromagnetic clutch.
Recently, needs for high speed processing in the image forming apparatus has been increased, and, accordingly, high speed sheet conveyance in the sheet conveying system has been requested more and more. However, the disadvantage of the conventional sheet conveying method in which the driving of the conveying rollers is ON/OFF by using the electromagnetic clutch is slow response of the electromagnetic clutch, which results in bottle neck for high speed sheet conveyance. On the other hand, as a drive source in a compact servo system capable of effecting open loop control, a stepping motor has widely been used.
The stepping motor is a motor in which a magnetic field is rotated by successively switching phase exciting electrical currents of windings and torque is generated by attracting and repelling magnetic poles of a rotor with respect to the rotating magnetic field thereby to rotate the rotor while being squeezed by the magnetic field. Accordingly, when the switching of the exciting phases is effected by inputting pulse signals, the stepping motor is rotated by a predetermined fundamental angle for each pulse.
Thus, in the stepping motor, the open loop control can be performed, and the system can greatly be simplified and cost can be reduced, in comparison with other servo actuators requiring a feedback system.
Therefore, also among the image forming apparatuses such as copying machines, there is an image forming apparatus in which the same number of stepping motors as the number of conveying rollers are used as drive sources in the sheet conveying system thereby to drive the conveying rollers without an electromagnetic clutch.
However, in the stepping motor, unlike to the conventional servo motor, although the motor can be manufactured in a compact and cheap manner, a phenomenon that the rotation of the rotor of the motor does not synchronous with the pulse signals may occur. This phenomenon is referred to as a phenomenon of loss of synchronism. In general, the phenomenon of loss of synchronism is generated in a overload condition regarding pulse rate supplied to the motor.
When the stepping motor is used in the sheet conveying system of the image forming apparatus, if the phenomenon of loss of synchronism is generated during the sheet conveyance, the sheet conveyance is stopped, which causes new sheet jam. Further, also in the sheet jam caused by the loss of synchronism of the stepping motor, since only the jam detection by the sensing of the sheet sensor can be effected, it is difficult to judge whether the sheet jam is caused by the loss of synchronism of the stepping motor or by other factors.
By attaching a sensor such as an encoder for detecting the rotation of the motor to the stepping motor to monitor the rotation of the motor, the loss of synchronism can be detected. In this case, however, the system becomes complicated not to utilize the merit of the stepping motor effectively. Accordingly, high speed detection of the loss of synchronism of the stepping motor without using the sensor gives great merit to the image forming apparatus.
Further, when the stepping motor is used in the sheet conveying system of the image forming apparatus, if the phenomenon of loss of synchronism is generated during the sheet conveyance, the sheet conveyance is stopped, which causes new sheet jam. On the other hand, in the sheet conveying system, the stepping motor is driven before the sheet reaches the associated sheet conveying roller. In the conventional sheet conveying system of the image forming apparatus, if the phenomenon of loss of synchronism is generated before the sheet reaches the conveying roller, after the sheet reaches the conveying roller driven by the stepping motor generating the phenomenon of loss of synchronism, the sheet is not conveyed, and, in this case, the sheet jam is detected.
Thus, even if the loss of synchronism of the stepping motor is generated and the associated conveying roller is stopped, so long as the sheet exists at that conveying roller, the stepping motor can be driven again and the arrival of the sheet can be waiting, which leads to enhancement of processing efficiency of the image forming apparatus.
The present invention is made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a stepping motor driving apparatus in which a phenomenon of loss of synchronism of the stepping motor can correctly be detected with a simple construction.
Another object of the present invention is to provide an image forming apparatus using a stepping motor to convey a sheet, in which a phenomenon of loss of synchronism of the stepping motor can positively be detected with a simple construction.
A further object of the present invention is to provide an image forming apparatus using a stepping motor to convey a sheet, in which interruption of sheet conveyance caused by a phenomenon of loss of synchronism of the stepping motor can be ceased to start sheet conveyance again efficiently.
A still further object of the present invention is to provide a stepping motor driving controlling apparatus which can detect a phenomenon of loss of synchronism quickly without using a detecting sensor for detecting the fact that a driven object is not moved.
A further object of the present invention is to provide an image forming apparatus in which, when a stepping motor is used in a conveying system of the image forming apparatus, a phenomenon of loss of synchronism of the stepping motor can be judged without using a sensor such as an encoder, and, if sheet jam is generated, it can be judged whether the sheet jam is caused by the phenomenon of loss of synchronism of the stepping motor or not.
A still further object of the present invention is to provide an image forming apparatus in which a phenomenon of loss of synchronism of a stepping motor can be detected, and, when the phenomenon of loss of synchronism is detected, if there is no sheet jam at a conveying roller driven by the stepping motor generating the phenomenon of loss of synchronism, processing efficiency can be enhanced by driving the stepping motor again after the stepping motor is once stopped.
That is to say, the present invention provides a stepping motor driving controlling apparatus for effecting driving by switching phase exciting of exciting electrical current supplied to an exciting coil of a stepping motor whenever a drive signal is applied to a motor drive circuit, which controlling apparatus comprises measuring means for measuring change in electrical current value flowing through the exciting coil of the motor for a predetermined time period, and control means for generating a signal of loss of synchronism when a measurement result of the change in electrical current value obtained by measurement of the measuring means during the predetermined time period exceeds a predetermined value.
A further object of the present invention is to provide a stepping motor driving controlling apparatus in which the change in electrical current value measured by the measuring means is an increasing ratio of electrical current flowing through the exciting coil.
A still further object of the present invention is to provide a stepping motor driving controlling apparatus in which supplying of the electrical current to the exciting coil of the motor is effected under constant electric current chopper control, and the change in electrical current value measured by the measuring means is chopping number of the electrical current within one phase exciting area of the motor.
A further object of the present invention is to provide an image forming apparatus using a stepping motor for effecting driving by switching phase exciting of exciting electrical current supplied to the exciting coil of the motor whenever a driving signal is applied as a drive source in a sheet conveying system, in which there are provided measuring means for measuring change in electrical current value flowing through the exciting coil of the motor for a predetermined time period set by a timer, loss of synchronism detecting means for judging that the loss of synchronism occurs when a measurement result of the change in electrical current value obtained by measurement of the measuring means during the predetermined time period exceeds a predetermined value, sheet detecting means disposed in a sheet conveying path of the sheet conveying system driven by the motor, jam detecting means for judging occurrence of jam if the sheet is detected by the sheet detecting means for a predetermined time period or if the sheet is not detected by the sheet detecting means, and control means for judging the occurrence of jam caused by the loss of synchronism of the motor if the jam is detected by the jam detecting means when the occurrence of the loss of synchronism is judged by the loss of synchronism detecting means.
A still further object of the present invention is to provide an Image forming apparatus having a loss of synchronism of a stepping motor detecting apparatus, in which the change in electrical current value measured by the measuring means is an increasing ratio of electrical current flowing through the exciting coil
A further object of the present invention is to provide an image forming apparatus having a loss of synchronism of a stepping motor detecting apparatus, in which supplying of the electrical current to the exciting coil of the motor is effected under constant electrical current chopper control, and the change in electrical current value measured by the measuring means is chopping number of the electrical current within one phase exciting area of the motor.
A still further object of the present invention is to provide an image forming apparatus using a stepping motor for effecting driving by switching phase exciting of exciting electrical current supplied to the exciting coil of the motor whenever a driving signal is applied as a drive source in a sheet conveying system, in which there are provided measuring means for measuring change in electrical current value flowing through the exciting coil of the motor for a predetermined time period, loss of synchronism detecting means for judging that the loss of synchronism occurs when a measurement result of the change in electrical current value obtained by measurement of the measuring means during the predetermined time period exceeds a predetermined value, sheet detecting means disposed in a sheet conveying path of the sheet conveying system driven by the motor, and control means for driving the motor again after the supplying of the electrical current to the motor is stopped, if the sheet is not detected by the sheet detecting means when the occurrence of the loss of synchronism is judged by the loss of synchronism detecting means.
The other objects and features of the present invention will be apparent from the following explanation of preferred embodiments referring to the accompanying drawings